Process of unhairing hides and skins



Patented Oct. 1, 1935 UNITED STATES PATENT OFFICE No Drawing. Application October 24, 1932, Serial No. 639,301

11 Claims.

This application relates to an improved process of depilating hides and skins and is a continuation in part of Serial No. 447,104 filed April 24, 1930.

An object of the invention is the depilation of hides and skins by a new process which removes many of the disadvantages of the old sulphide treatment and yet operates in a much more rapid cording to the manner in which the products were used, a valuable by-product of the hides and skins, viz. the hair was damaged or even completely disintegrated, owing to the destructive action of the sulphides, especially sodium sulphide. At the same time, owing to the drastic action of the sodium sulphide. the grain of the hides or skins was spoilt, becoming roughened, and also, owing to a loss of hide or skin substance, the resultant leather showed looseness and depletion. This was of great disadvantage for the production of the finest leathers, and, indeed, for these the old lime process is still largely used today. So, then, processes are in use today which embrace, on the one hand, the relatively mild, slow method using lime only and often requiring many days, and, on the other hand, the very rapid. way of unhairing using sodium sulphide alone and requiring but a few hours. Between these two extremes with their corresponding disadvantages, various combinations of lime and sodium suphide are being used, giving results of varying degrees of rapidity and severity. It is significant that lime alone gives, on the one hand, hair of good quality, a smooth grain and fullness of leather but too slowly, and, on the other hand, with an excess of sodium sulphide the hairis totally destroyed and the leather has a looseness combined with a harsh or raised grain. So far, in a general way, it has not been found possible to use a combination method to give all the advantages and none of the disadvantages. The tanner has had to effect a compromise between an economy of time and labor and of quality of leather.

Various improvements have been suggested from time to time. These have been attempts to modify in some manner the drastic action of the usual alkali sulphides. Carmichael in British Patent #173,788 of January 3, 1922, by using a small amount, viz. a solution of sodium sulphide for heavy hides and then placing them in a solution of caustic soda, claims certain advantages with respect to less loss of hide substance and a smoother grain. However, he takes no account of the use of lime and employs only caustic soda as a swelling agent, which is not satisfactory for the production of the best leathers on other types of skins.

Bergmanri-British Patent #222,121 of 1925; German Patent #432,686 of 1926; D. R. 1?. #434,570 of 1926; U. S. Pat. #1,599,358 of 1926- has proposed to modify the action of sodium sulphide bydecreasing the hair destroying and skin swelling capacity. However, the skins are afterwards subjected to routine methods, and examples are given of the use 'of lime and sodium sulphide paints which nullify any good effect obtained in the pretreatment, and the methods refer only to sulphides of nitrogen bases or to nitrogen bases alone. Again, according to U. S. Patent #1,743,938 of Edw. A. Taylor, the harmful effects or the drastic action of sodium sulphide may be modified by the incorporation of a certain amount of sodium sulfhydrate, whereby overplumpness and harshness of grain may be avoided. However, according to the practice as given in the patent, the hair is entirely destroyed, and the sulphide mixture is used in combination with lime.

The present invention relates to a method of employing all sulphides in such a manner that the harmful effects are entirely obviated, and yet the process is considerably more rapid than that of the old liming process. I have found that in the use of sulphides, hair loosening and hair destruction are distinctly different types of action, and that by suitable means the hair destroying capacity can be entirely suppressed, thus allowing the hair loosening or-true depilating action to proceed. I have found that by suitably adjusting the alkaline reaction of the sulphide solution employed to a pH value of not over 12.2 determined calorimetrically, or a pH value of not less than 11.8, there is a differentiation in the action of the sulphide, in that the epidermis is attacked and weakened on the one hand, whereas, on the other hand, the material of the hair, or true keratin, and the hide substance proper, viz. the collagen, appear not to be attacked. In other words, the pH of the sulphide solution lies between 11.8-12.2.

On placing hides and skins, after the usual soaking treatment, in such a modified sulphide solution for a period of about 6 to 24 hours, the hair is very decidedly loosened so that it may easily be pulled out by hand, and the epidermis is loosened and may readily be removed by scraping with the finger. At the same time the hair is not attacked and on removing brings with it the complete hair bulb together with the inner hair root sheath. Then on draining and, if necessary, washing and placing these hides or skins in a suspension of lime, such as is used in the leathermaking industry but containing no sulphides, the depilatory action of the lime is markedly increased, so that the hair slips readily in from 24 to 72 hours, according to the nature, class and cure of the hides or skins. grain is smooth and silky, there is no excessive loss of leather-forming substance, and the hair is in a good undamaged condition. This refers to all manner of sulphides of bases whether of inorganic or organic nature.

Such a modified sulphide solution may be prepared from an alkaline sulphide, e. g. sodium sulphide, in the following ways:

(1) The alkaline sulphide may be used in small concentration such that the alkalinity of the resultant solution lies between that represented by a pH equal to 11.8-12.2.

(2) The action of a solution of an alkaline sulphide may be modified by reducing the alkalinity to that represented by a pH of 11.8-12.2:

(a) By the addition of an appropriate quantity of the sulfhydrate of an alkali or alkaline earth, such as sodium sulfhydrate, potassium sulfhydrate, barium sulfhydrate, calcium sulphhydrate.

(b) By the addition of an appropriate amount of an acid, such as sulphuric, muriatic, acetic acid, phosphoric, boric, formic or any organic carboxylic or sulfonic acid.

(0) By the addition of an appropriate amount of an acid salt, such as sodium bicarbonate, sodium bisulphite, sodium bisulphate, mono sodium phosphate, sodium acid tartrate, potassium acid phthalate, potassium acid succinate.

(d) By the addition of the appropriate amount of a soluble salt, which on dissolving in water gives a solution having an acid reaction, such as aluminum sulphate, aluminum chloride, chromium chloride, pyridine hydrochloride, hydrazine sulphate, hydroxylamine hydrochloride.

(e) By the addition of an appropriate amount of a soluble salt of aweaker base, such as am-' monium sulphate, methylamine hydrochloride, ethylamine sulphate, propylamine acetate.

As examples of the above:

(1) 1,000 lbs. green weight of hides or skins, after the customary soaking, is inmiersed in a suitable vessel containing 600 gals. of water, in which are dissolved 7 lbs. of sodium sulphide on 100% basis, or 12 lbs. of sodium sulphide of 60% strength, at a temperature of 70 F. for a. period conveniently overnight- The hides or skins are now removed from the liquor, drained or washed, and then placed in a vessel containing 600 gals. of water in which 100 lbs. of hydrated lime is presexit. The temperature is preferably maintained at 70 F. After a period of one to three days the hair slip is satisfactory and the hair is in good condition. The hides or skins may be unhaired by hand or by some mechanical process.

similar results may be obtained by using in the liquor given before the liming treatment the following bath compositions and operating in the same manner as above; 1

At the same time the (2) 13. lbs. of sodium sulphide on 100% basis, or 27 lbs. of sodium sulphide 60% strength, and 34 lbs. of sodium sulfhydrate.

(3) 50 lbs. of sodium sulphide of 60% strength and 15 lbs. of sulphuric acid of approximately 5.

98% strength.

(4) 22 lbs. of sodium sulphide on 100% basis, or 37 lbs. of sodium sulphide 60% strength, and 17 lbs. of sodium bicarbonate.

(5) 24 lbs. of sodium sulphide on 100% basis, or 40 lbs. of sodium sulphide of 60% strength, and 18 lbs. of crystallized aluminum sulphate.

(6) 21% lbs. of sodium sulphide on 100% basis, or 36 lbs. of sodium sulphide of 60% strength, and 9 lbs. of ammonium chloride.

The'subsequent operations of bating, pickling and tanning are in no way interfered with or changed by the above processes.

Similarly, with any other soluble sulphides of strong bases, for example potassium sulphide, barium sulphide, their caustic nature may be modified in a similar manner to that of the alkaline sulphides. On the other hand, in order to increase the depilating power of sulphides of weak bases, for example, methylamine sulphide, ammonium sulphide, when used in this manner," the alkalinity may be brought to the corresponding point by the addition of small amounts of alkalies, alkaline earths, alkali and alkaline earth salts of .weak acids, and, basic salts, provided that the alkalinity of the resultant solution is not great-- er than that represented by a pH of 12.2.

As an example:

Using the same quantities of hides or skins as given before, an immersion in a liquor containing 50 lbs. of ammonium sulphide on 100% basis, or 300 lbs. of technical ammonium sulphide of 16% strength, and 5 lbs. of caustic soda may be given before the lime treatment.

Equivalents of the materials mentioned above can be used to good advantage and are included herein.

For practical convenience, in tanneries where chemical control is very often not available, we have found that a dry powder can be manufactured and used for the purpose before-described. This has the advantage for the tanner that it,is

a of uniform composition, and, the pH being regulated, the unhairing results are consequently uniform from batch to batch and day to day.

As examples of these products, the following will suffice:

A dry, powdered mixture of sodium sulphide, 90% strength, 100 lbs., sodium bicarbonate 70- lbs., or in place of the bicarbonate, sodium 55 bisulphite -95 lbs. can be used.

If desired, the above products can be dissolved in water and then dried out. Of course, equivalents of these amounts may be substituted.

In the application of this invention I am not limited as to time, temperature, concentrations or materials, proportions of liquors to hides and skins and type of vessel, and the foregoing examples are merely given to illustrate the inven- 65 tion, and they may be adjusted to conform to the type and cure of the skins or hides and the type and character of the particular leather being manufactured. Thescope of the invention is limited only by the following claims, no modiflca- 7 pH 01' 11.8-12.2, washing and immersing them in a lime liquor.

2. In the process of depilating hides and skins, the steps which comprise immersing them in a solution oi a sulphide to which a sulthydrate has been added, so that the alkalinity of the resultant solution is represented by a pH of 11.8-12.2,

washing and immersing them in a lime liquor.

3. In the process of depilating hides and skins. the steps which, comprise immersing them in a solution of a sulphide to which an acid has been added, so that the alkalinity of the resultant solution is represented by a pH oi! 11.8-12.2, washing and immersing them in a lime liquor.

. 4. In the process of depilating hides and skins, the steps which comprise immersing them in a solution of a sulphide to which an acid salt has been added, so that the alkalinity of the resultant solution is represented by a pH of 1l.8-l2.2, washing and immersing them in a lime liquor.

5. In the process of depilating hides and skins, the steps which comprise immersing them in a solution of a sulphide to which a soluble salt which gives an acid solution has been added, so that the alkalinity of the resultant solution is represented by a pH oi! 1l.8-l2.2, washing and immersing them in a lime liquor.

6. In the process of depilating hides and skins,

the steps which comprise immersing them in a solution of a sulphide to which a soluble salt of a weaker base has been added, so that the alka- I linity ot the resultant solution is represented by a pH of 11.8-12.2, washing and immersing them in a lime liquor.

7. In the process 01' depilating hides and skins, the steps which comprise immersing them in a solution of a sulphide to which has been added a substance to regulate the pH to 11.8-12.2, washing, and immersing them in a lime liquor.

- 8. In the process of depilating hides and skins, the steps which comprise immersing them in a solution of an alkaline sulphide of a pH of 11.8-12. 2 washing, then immersing them in a limeliquor.

9. In the process of depilating hides and skins, the steps which comprise immersing them in a solution of an alkaline sulphide to which an alkaline sulfhydrate has been added to regulate the pH at 118-122, washing, then immersing them in a lime liquor.

10. A process as described in claim 8 in whichsodium sulphide is the sulphide employed.

11. A process as described in claim 9 in which 25 sodium sulphide is the sulphide employed.

HAROLD G. TURLEY. 

